Lamp with arc preventing fuse



Aug. '24, 1937. v M, v 2,091,233

LAMP WITH ARC PREVENTING FUSE Filed Jan. 4, 1935 INVENTOR I ATTORNEYPatented! Aug. 24, 1937 UNETED STATES gonna PATENT OFFICE acetate LAMPWITH ARC PREVENTING FUSE Application January 4, 1935, Serial No. 416

Claims.

This invention relates to devices such as lamps, radio tubes and similardevices, and more particularly to an improved base structure for suchdevices.

It has been found that one of the most serious defects in lamps of thetype having a fuse in the base is in the production of destructive arcsin the lamp base. This is true in the case of mechanically based lamps,that is to say lamps where the metal shell contact base is fastened tothe lamp bulb without the use of cement or similar bonding materials,and more especially true where such mechanically based lamps have one orboth of the lead-in wires of fuse metal. Thus in this latter type oflamp there is a considerable exposed area on the inner face of the metalshell,

I, and when the fused lead-in wire blows, the resultant metallic vaporsand ions tend to strike an arc to the exposed area of the shell. Onemethod of reducing the possibility of such destructive arcing in thecase of cement-based lamps is disclosed in application Serial No.750,473, filed October 29, 1934. Another method that has been proposedis to provide the fused lead-in wire with a tubular T covering ofasbestos or the like.- However, in

practice it has been found that because of the practical difliculty ofmaintaining the tubular insulator in intimate contact with wire and withthe eyelet in the lamp base, there is usually present an unobstructedpath for the striking of an are between the eyelet and the metal shell.I have found that in order to prevent such destructive arcing, itisnecessary to insulate completely the eyelet from the interior of theshell.

Accordingly one ofthe principal objects of the present invention is toprovide a lamp or tube having a fused lead-in wire, and wherein thechances of destructive arcing in the base are substantially eliminated.

A feature of-the invention relates to a lamp ing a contact base of thethreaded metal shell and insulated metal button type, wherein the eyeletin the metal button contact is completely protected against theformation of destructive arcs interiorly of the shell.

A still further feature relates to the'novel organization, arrangementand relative location of parts which go to make up a mechanically basedlamp which is substantially entirely free from the dangers ofdestructive arcing in the base thereof.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

While the invention will be disclosed herein as embodied in oneparticular type of mechanically based lamp, it .will be understood thatthis is done merely for purposes of explanation and not by way oflimitation, and furthermore only those parts of the lamp are shown asare sufficient to enable the inventive concept to be thoroughlyunderstood.

Referring to the drawing, numeral I indicates the neck portion of anenclosing envelope of any well known shape such as is employed in lamps,radio tubes or the-like. Preferably, although not necessarily, the neckI terminates in a threaded butt 2, whichhas a series of threads moldedtherein, and is also provided with a uniform flat annular shoulder 3.Threaded on tothe butt 2 is a correspondingly threaded metal shell 4which has insulatingly fastened thereon a metal contact button 5provided with an eyelet 6. In accordance with the usual practice, thebutton 5 is fused or otherwise fastened to a hollow glass plug 1provided with a circular flange 8 fused or otherwise fastened to thebottom wall 9 of the shell 4, it being understood that the said wall 9is provided with a circular opening to receive the plug 1.

One of the lead-in wires it passes through the eyelet 6 and is solderedthereto, thus closing said eyelet. The other lead-in wire II may be bentback over the rim of butt 2, and soldered or otherwiseconductivelyconnected to the shell 4. Any well known means may be provided forpreventing relative turning movement between shell 4 and butt 2. Thus asindicated in the drawing, one of the threads of butt 2 is provided witha series of grooves which are adapted to be filled with a. fusible metalwhich effectively bonds the butt to the metal shell. For a detaileddescription of this type of mechanical basing, reference may be had toapplication Serial No. 758,349, filed December 20, 1934.

In accordance with the present invention, one of the lead-in wires,preferably the wire 10, has a portion of its length constituted offusible metal, so that when excessive current tends toflow throughthelamp the said lead wire blows and breaks the circuit through thelamp. In lamps of this type as will be noted, there is a considerablylarge area on the inner face of shell 4 which is left exposed to thelead wire I0. Furthermore the eyelet 6 and the corresponding opening inplug Imust be of considerable size in order to facilitate threading thewire l0 through the said eyelet. Consequently, when the solder I2 isapplied, there is left exposed to the interior of the shell 4 arelatively large metallic area. It has been found that when the lead-inwire l blows, the resultant metallic vapors, metallic particles andmetallic ions, tend to strike an are between the exposed area of shell4, and the exposed area of the eyelet 6, and this is true even where thefused lead-in Wire is provided with an insulator tube since there isalways a space left between the wire and inner wall of the tube, and inalso a small space between the end of the tube and the eyelet. Inaccordance with the present invention, eyelet 5 is provided with acompletely protective insulating filling, so that there is no exposedmetal, apart from the lead wire itself, to .5 which a destructive arccan strike. Preferably this protection is afforded by embedding thelead-in wire in an insulating material l3 which completely fills theinterior hollow portion of the glass plug 1, the depth of the filling 13being preierably proportioned so that the length of the embedded wire I0is related to the impressed voltage at which the lamp is designed tooperate, for purposes about to be described. The insulator i3 ispreferably of such material that it is capable of being bonded directlyto the glass 1 upon the application of suitable heat, or if desired acoating of suitable insulating bonding material may be applied to theinner surface of the glass plug '1, so that upon the assembly of theinsulator I3 39 and upon heating and drying, the said insulator I3 isintegrally bonded to the glass 1 thus cornpletely covering the otherwiseexposed area of the eyelet B. The insulator l3 may be prepared from thefollowing materials: 85.0 gms. of marble flour, 3.5 gms. of rosin, 4.5gms. of shellac, 7.0 gms. of resin and 10.00 cc. of alcohol, The resinis a heat hardening resinoid such for example as bakelite or durite. Itwill be understood of course that any well known manner of applying theinsulator i0 E3 to the wire I! may be employed. For example, the saidinsulator may be previously shaped to correspond to the shape of thehollow portion of plug 7, it being understood that the lead wire ID haslikewise been previously embedded in the said insulator I 3. Preferablyhowever, the material i3 is applied to the shell in a semi-plastic massso that the wire [0 may be pushed readily through the mass and thensoldered to the eyelet ID in the usual manner. When the base is heatedthe wire is imbedded in the mass which solidifies and bonds itselfintimately to the members 6, l and I0. It has been found that the bestresults are obtained if the insulating material I3 is such that uponbeing dried or baked it solidifies into a somewhat porous mass so as tocause the gas or hot vapors resulting from the blowing of the fuse, tobe dispersed through the body of the porous mass before a destructivearc can be maintained.

With the above described arrangement, should the fuse lead-in wire l0blow, the portion thereof which is not embedded in the insulator l3fuses and if an arc should thereafter strike between the shell 4 and theexposed tip of the wire I0 where it enters the insulator l3, the currentrequired to maintain this are must pass through the remainder of thewire I0 which is embedded in the insulator. However before this are canbe destructive the remainder of the fuse in the insulator l3 will blowand because of the porous character of the insulator l3 the metallicvapors and gases are forcibly dispersed in nonlinear paths through andinto the pores of the insulator before they have a chance to follow upthe previous path of the fuse. Preferably the thickness .of the memberl3v and consequently the length of the embedded fused wire and theporosity of said member l3 are chosen so that for the voltage involved,the arc cannot follow the previous path of the fuse. Thus the lamp iseffectively protected against the formation of destructive arcs betweenthe eyelet G and the shell 4.

Various changes and modifications may be made herein without departingfrom the spirit and scope of the invention. A continuation-inpart of thepresent application has been filed September 17, 1935, as applicationSerial Number 40,871.

The lamps of the following claims obviously include only those lampswhich, in the absence of a fuse or similar protector, would besusceptible to arcing at burnout. For the purpose of this specification,a cement is defined as a material which can be applied to the base in asemiplastic condition and which, on heating, solidifies into a porousmass intimately bonded to the surrounding materials.

What I claim is:

1. In combination a lamp having a metal shell base, a metal contactbutton normally partially exposed to the interior of the metal shell andinsulatingly carried by said shell, a lead-in wire having at least partof its length formed of fuse wire, said lead-in being connected to saidbutton, and insulator means of porous cement to insu late said buttoncompletely from the interior face of said shell, said fuse Wire having apart only of its length directly embedded in said porous insulatingcement.

2. An electric lamp comprising a bulb, a contact base afiixed to saidbulb, and lead-in wires from said base to said bulb, said basecomprising a substantially cylindrical metal shell whose interiorsurface is exposed to the atmosphere inside the base, a cup-like glassplug closing 05 the end of said shell, a perforation through said plug,a metal contact button having an eyelet in registry with said plug, alead-in wire attached to said eyelet and including a fuse wire directlyembedded in a mass ofporous, insulating, arcquenching cement whichinsulates the eyelet from the atmosphere of the interior of the base byall paths except through the fuse.

3. An incandescent lamp comprising a bulb, a hollow metal shell base,the interior of whose metal shell is exposed to the atmosphere insidethe base, a lead-in wire including a fuse and extending from said bulbto an eyelet contact carried insulatingly by said shell base, said fuseand eyelet being both inside a single sheath of insulating material toinsulate them from the atmosphere of the interior of the base by allpaths except through the fuse.

. 4. A lamp as in claim 3 in which the metal shell base is of themechanical type.

5. An incandescent electric lamp comprising a bulb, a hollow metal shellbase of the mechanical type in which the interior of the metal shell isexposed to the atmosphere inside the base, a lead-in Wire including afuse wire extending inside said base to an eyelet contact carried by aninsulating plug forming part of said base, said fuse wire being directlyembedded in a mass of porous, insulating, arc-quenching cement bonded tothe insulating plug which carries the eyelet contact, said. cementserving also to completely insulate the eyelet contact from theatmosphere inside the base.

ROLLAND M. ZA'BEL.

